Lithium-ion (Li-ion) batteries have been widely used for portable electronics, and they are being intensively pursued for hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs), electric vehicles (EVs), and stationary power source applications for smarter energy management systems. The greatest challenges in adopting the technology for large-scale applications are the energy density, power density, cost, safety, and cycle life of current electrode materials. Of all the properties, the charging time is the most important characteristics for the battery as well as the power density, especially as the application targets of Li-ion batteries move from small mobile devices to transportation. This is because EV users, for example, are hardly to wait more than half an hour to charge their vehicles during a long drive compared with a refueling period of less than 5 min for gasoline cars. The power performance of lithium ion battery is greatly affected by the conductivity of both anode and cathode materials, which rely on conductive additives.
Carbon based conductive additives such as carbon black and acetylene black are the commercially available. However, a uniform distribution of these carbon based conductive additives in a binder is always suppressed due to aggregation of the additives; as a result, the charging speed is hardly improved. Other kinds of carbon materials such as carbon nanotubes (CNTs) and carbon fibers also have difficulty to improve the kinetics in economically and effective way.
Graphene, which is base of all graphitic structures, offers an attractive substitute for all other kinds of carbon materials. Graphene is distinctly different from CNTs and fullerenes. Graphene and chemically modified graphene sheets possess a high electrical conductivity, high surface area, and outstanding mechanical properties comparable with or even better than CNTs. The specific surface area of a single graphene sheet is 2630 m2/g, which is much larger than those of activated carbon and CNTs that are usually used in the electrochemical double layer capacitors. These characteristics make graphene a most promising material for energy storage related applications.
U.S. Pat. No. 8,691,441 proposes graphene-enhanced cathode materials for lithium batteries and the graphene-enhanced cathode materials are composite materials to increase the conductivity of cathode materials. WO2012/048194 discloses nanocomposite anode materials with chemically reduced graphene. CN103682368 discloses porous structure of a three-dimensional graphene network as a conductive agent, which is deposited with cathode materials to build a flexible and fast chargeable lithium ion battery.